Piezo-electric stereo transducer



April 2, 1963 TAKEO SHIGA PIEZO-ELECTRIC STEREO TRANSDUCER 2 Sheets-Sheet 1 Filed April 22, 1960 [fir En far" Eeo S/wga h, MM

April 2, 1963 TAKEO SHIGA PIEZO-ELECTRIC STEREO TRANSDUCER 2 Sheets-Sheet 2 Filed April 22, 1960 'III $5 792 d 30 {9'4 by 1 51/ 75- Japan Filed Apr. 22, 1960, Ser. No. 24,079 Claims priority, application Japan Feb. 6, 1960 2 Claims. (Ql. 179-'-100.41)

This invention relates to a piezo-electric transducer device and more particularly to such a transducer device for performing an electromechanic transformation based upon the piezo-electric phenomenon of a piezo-electric crystal such as Rochelle salt.

One object of this invention is to provide a piezo-electric transducer device in which a piezo-electric element which is cut out from a piezo-electric crystal with a certain angle with respect to a crystal axis is subjected to bending and torsional vibrations to obtain an electrical voltage which is proportional to the sum or the difference of the vibrations.

Another object of this invention is to provide a piezoelectric transducer device in which a piezo-electric element which is cut out from a piezo-electric crystal with a certain angle with respect to a crystal axis is subjected to two kinds of oscillatory voltage to obtain two kinds of mechanical vibrations which are respectively proportional to the sum and difference of the oscillatory voltages.

A further object of this invention is to provide a Bitnorph type piezo-electric transducer device which is available to cut a so-called 45-45 system stereo record or to a pickup for reproducing sounds from a 45-45 system stereo record.

A still further object of this invention is to provide a piezo-electric transducer device in which the transformation characteristics can be improved by using such a Bimorph. g

Other objects, features and advantages of this invention will be apparent from the disclosures in the specification and the accompanying drawings:

FIG. 1 is a diagram illustrating the relationship between States Patent X ==shearing force along the Y-axis on the plane perpendicular to X-axis Then the piezo-electric element will produce piezo-electricity resulting from bending and torsion based upon the shearing force. For instance, if P is the polarization produced on the surface perpendicular to X-taxis, by way of example, due to the shearing force Y the following formula is obtained to the faces 2 and the minor axis BB perpendicular to the axis A-A' are respectively inclined to the Z-ax-is and Y-axis by an angle 0 as shown in FIG. 1.

In order to consider the polarization of the above element 1, explanation will be taken in the case in which the element 1 is subjected to the shearing force Y in connection with FIG. 2 which illustrates the element seen along the X-axis.

If a perpendicular compression force P and a shearing force F along the side face 2 are applied to the element 1, the polarization P due to the perpendicular compression force F is produced on the x-face per unit area thereof and the polarization P due to the shearing force is equally produced on the same face. The polarizations can be expressed by'the'following formulae:

a shearing force applied to a piezo-electric element and a voltage produced thereby which is referred to as piezoelectric voltagehereinafter.

MG. 2 is a plan view seen along the X-axis in FIG. 1 for illustrating the same relationship as in FIG, 1.

FIGS is an electrical explanatory view of a piezo-electric element which is arranged to produce a piezo-electric voltage due to the shearing force.

PEG. 4- is a perspective view of a piezo-electric transducer'device, byway of example, forming a Bimorph according to this invention.

FIG. 5 is a diagrammatical representation for illustrating a so-called -45 system stereo recording.

7 PEG. 6 is a cross-sectional side view of a pickup according to this invention.

Ifthe forces F and F are simultaneously applied, then the polarization, P becomes:

Now, if the polarization, P is to be proportional to the sum and difference of the a1'Jplied'forces,'F and P the following relationship should exist:

3 tion of the angles of polarization of the two crystals mak- FIG. 7 is a partial enlarged perspective view of Bi'morph Y =shearing force along the Z-axis on the plane perpen.

dicular to Yaaxis Z =shearing force along the X-axis on the plane perpendicular to Z-axis ing up the Birnorph, a voltage can be derived which will be proportional to the sum or difference of the two active forces. Thus, when the first crystal has an angle 6 existing between its angle of polarization and the major axis of the crystal, the angle ofpolarization of the second crystal should be such that it is different from the polarization angle of the first and makes an angle with its major axis which satisfies the equation:

cos 0 sin 0:: (cos 0--sin 0) Mathematically, there are the following solutions for this polarization angle:

(frequency v=%; w=angular velocity) the following voltage can be obtained; acrossa load resistor R connected, between the electrodes 4 and; 4.:

' =i wQ Q'= z x= 1 14Yz where,

Y ==F cosa sin ='=FC in the case of F Yz= s 0 n '6 )'=F; in the case of F yand Y =F cos 0 sin 0 F3 (cos n sm 0): (Ff-{11 16 in the case of F andF where, i

S=area of theelectrode 4 K =dielectric.coeflicient a=thickness of the crystal i=\/- 1 i The absolute value of V can bezexpressedz F511) "w 1 +(RC"fw) 0:: capacity of the element.

As seen-from the foregoing description, the "voltage which is proportional to thesumor' the difference'of the two forces P and F can be -obtained if the formula cos (i-sin 0= i (cos .0sin 0) C. is satisfied when the forces Fe and "E ware-'applieii'to the element 1. I

Although the previous description has. been taken for explaining the principle of this invention in the case where the polarization'isproducedby 'the shearing forced!" and the piezo-electric voltagejszproduceddue to the polarization, external forces appliedtotheelement in any desired directions are equally cdrisideredjto be analyzed as the forces "F and F Accordingly the analyzed forces F ana F will'be applied to'the element 1, which causes the-sarne polarizations and a the corresponding piezoelectric voltage as those'alreadydescribed in the former example, if the angle-B 'in this c'as'eis adequately selected, Hence, if external force'ssu'ch as bending and torsional forces are appliedfto the element '1, the same is, in turn, subjected to the forces Fe and F corresponding thereof so 'th atan electrical signal which is proportional to'the sum or the difference of the, bending and torsional forces can be obtained from the element. A

Now, apiezo-e'lectric t'ransducerdeyice, byway. or ex-. ample, according to this invention will be explained in connection with a piezo-electric element 1 as shown in FIG. 4 which shows a perspective view of a piezo-electric body 1 which is generallyl'refe'r red toes a Bimorph composed of oblong piezo-electric eleme'hts 1a and 1b. The angle constructed by the Z-axis and-the longitudinal axis AA of the oblong elerrient's ia and 1b is the angle 0 which satisfies the above 'n'ientiond condit-ions. The Bimorph is made. by attaching the oblong, elements 1a and 1b, one being upset to the other and an electrode 5 being sandwiched therebetween. The full line Y-axis and Z- axis are the crystal axes of the element 1a and the dotted line Z-vaxis and Y-axis are the crystal axes of the element 1b. By the above construction, the piezo-electric voltage which stands for P -l-P can be produced across the electrodes 4a and '5 for the element "1a, while the piezo-electric voltage which stands for P, ,P can be obtained across the electrodes 4b and 5.. I

Now, one end of the Bimorph in the axis AA' is secured to a stationary part, while oscillatory moment and up and downward vibration or bending are applied to the other end of the Bimorph as shown by the arrows in the drawing. Then the piezo-electric elements 1a and 1b will be subjected, to the forces corresponding to E, and F Accordingly, if the angles 0 are so selected as to satisfy the conditions above referred to, one of the ele rnents will produce the voltage which is proportional to the sum of the magnitudes of the moment and bending and' the other will produce the voltage which is propor tional to the difference between the magnitude of the moment and that of the bending.

The above mentioned Bimorph type piezo-electric element 1 will be adapted for a stereo pickup. In the stereo pickup, the perpendicular and horizontal vibrations of a stylus are simultaneously applied to the element 1 so that the vibrations are transmitted to the piezo-ele'ctric element as the bending and torsional forces, if an adequate transmission means are adopted between the elements and the stylus. It will be apparent in this case that the ele merit In and lbwill produce the voltages which are respectively proportional tothe sum and the dilferenceof the perpendicular and horizontal'vibrations, if the angles Q are so selected as tosatisfy the above mentioned conditions.

The description will be continued in connection. with a pickupfembodying this invention which is'adopted for reproducing sounds. from the groove of a, stereo record. FIG. 5 shows a diagrammatioal representation for the relationship between a groove of. the stereo record and a stylus of a so-called 45-45 stereo system the groove consisting of the left groove; pant 7a and the right groove part 7b whichare-respectively inclined by 45 degrees with respectto the surface of the record. The left, and the right groove parts have. respectively two kinds of the signals which are recorded in the grooves with the stereo relationship. A- stylus vibrates in the vertical and horizontal directions when itis guided by the groove.

FIG. 6shows a sectional view of such a stereo pickup embodying this invention. 9 illustrates generally a cartridge. 11 is a tubular insulation case which is covered with a cover 10 and which has an opening 13 communicating with a hollow chamber 12 and the atmosphere,

In the chamber 12 is so arranged a Bimorph type piezoelectric element 1 according to this invention that the xface of the Bimorph is substantially in the horizontal plane and the A- A' axis is substantially parallel to the axis of the cartridge 9. To the front end of the Bimorph 1 is mounted an armature 14 which is shaped as substantially an isosceles triangle in such a manner that the Bimorph is inserted into a window 15 formed on the armature and that the Bimorph is arranged on the plane perpendicular to the-axis 1}-A of the Bimorph 1, as shown inFIG. 7. The apex of the armature 14 has a recess 16 which is preferably formed as reverse V as shown in FIG. 7- On the frontend of the piezo-ielectric element 1 is attached a supporting piece 17 one end of which --is secured to the case 11 as shown in FIG. 6-. The Bimorph type piezoelectric element 1 issuppor ted by dampers 18 ofany suit-. able resilient material which are pressed on the x-face of the element; substantially on the horizontal plane. The

supporting piece 17 is preferably made of a sheet of synthet'ic resin such as nylon sheet having a suitable resilient property. The supporting piece has a {fork shaped end to which the end of the Bimorph 1 is inserted and adhered thereto by suitable binder as shown in FIG. 7. The other end of the supporting piece is preferably supported and compressed by the two parts of the case 11. At the rear end of the case 11 is provided a pair of leading pins 19a and 1917 which are respectively connected to the electrodes 4a and 4b ofthe element 1a and 1b respectively through lead Wires 20a and 20b. The common electrode 5 of the Bimorph type piezo-electric element 1 is connected, through a lead wire 21, to a conductive connection ring 22 which is attached to the rear end of the case 11. The lead wire 21 is connected to a pickup arm which is connected to the pins 19a and 1%.

On the lower part of the case 11 is mounted a stylus supporting member 22 to which one end of a resilient bar 24 is secured by a bifurcated element 25 and a screw 27 passing therethrough. The other end of the resilient bar 24 is connected to a stylus bar 23 which is supported by the armature 14. 29 is a damper supporting the stylus bar 23. The stylus bar 23 is preferably made of a tubular member which is made of a comparatively hard metal and which has a small diameter.

The stylus bar has a flat shaped portion 26, at its free end to which a stylus 8 is held. The resilient bar 24 is preferably made of a resilient string such as a piano string one end of which is inserted and secured by a suitable binder to the stylus bar 23.

The bifurcated element 25' is secured to the conductive connection ring 22 by the screw 27 as already referred The Bimorph element 1 is arranged in a cartridge 9 as noted above, with one :of the elements having an angle ranging from 0 to 45 between its axis A-A and its Z-axis, and the other of the elements may have an angle of 90+(0 to 45). For example, one may have an angle of 22.5 and the other (90+22.5). It is more practical, however, to make a Bimorph according to this invention in which one element has a polarization angle with respect to the long dimension of the element which is equal and opposite with respect to the polarization angle of the other element to which it is laminated.

In this case, if V and V respectively represent the output voltages produced across the pin 19a and the ring 22 due to the horizontal and vertical vibration of the stylus for one element 1a and V and V those for the other element 112, the 0 can be so selected that the condiiioils 1n= 1v; V2H: V2V 0r rrr=- ivi 2n= 2v are satisfied. Accordingly if a Bimorph is made by combining two similar piezo-electric elements, one being upset with respect to the other, the Bimorph satisfies the conditions V =V and V =-V so that one of the elements 1a produces the voltage V -V or V +V and the other element 1b produces the voltage V +V or V V It will be apparent that the stylus 8 vibrates in the vertical and horizontal directions along the grooves 7a and 7 b which are respectively inclined by 45 with respect to the surface of the record and that the armature 14;

is driven through the rod 23 with the result that the Bimorph elements 1a and 1b are subjected to the bending and torsional forces due to the vibrations to produce the electric voltages which satisfy the above mentioned condi' tions from the elements. That is, if the stylus moves to the left in 45 direction in an instant, the elements 1a and 1b respectively produce, as the resultant voltages V -i-V and V -V but only the element 1a produces V +V because of the fact that V =V and the element does not actuate in this movement. Similarly,- if the stylus moves to the right in 45 direction, only the element 1b produces, as the resultant voltage, V -l- V and the element 1a does not actuate in this movement.

Accordingly these voltages can be led out from the leading pins. 1

The two kinds of the electrical output are stereo signals.

In general, a piezo-electric element made of Rochelle salt has comparatively lower resonant frequency (of the order of 5,000 or 7,000 cycles per second) according to its shape when adopted for a pickup.

This due to its physical properties. Accordingly such a piezo-electric element lacks good frequency characteristics and mechanical recovering property so that it can not follow an electrical transient property. Moreover, Rochelle salt has less mechanical strength so that it is difficult to make a Rochelle salt piezo-electric element having a very small thickness. This is also true due to the fact that it is desired to increase the inner capacity in order to improve frequency characteristics. To overcome such difficulties, glass or metal plates 28a and 28b, each having the thickness of 0.24.5 mm. for example and greater stiffness as compared to that of the piezoelectric elements la and 1b, are respectively attached to both the side surfaces of the Bimorph elements as shown in FIG. 10, or a thin plate 28 is sandwiched by the elements 1a and 112 so as to integrally form the Bimorph.

By these means the stiffness of the Bimorph is increased and the resonant frequency becomes higher. Besides, such constructions serve to avoid the fatal defect that the Rochelle salt is weak mechanically.

In order to transmit the displacement or vibration of a stylus which is fitted to a groove cut in the direction of 45 with respect to the record surface to piezo-electric elements through an armature, it is required that the transmission mechanism have the same strength and the same elasticity with respect to the vertical and horizontal vibrations within the desired frequency band. To this end, it is also required that the resonant frequency of the vibration system is selected possibly higher for a higher frequency range and the mechanical resistance thereof is selected possibly lesser for a lower frequency range. V

Moreover, the transmission is needed to actuate at the same conditions in the case of applying vertical and horizontal vibrations thereto. In this case undesirable resonant parts must beeffectively damped. To satisfy the above conditions the stylus rod 23 is made of a thin pipe of comparatively hard and light metal such as Duralumin as has been described. The stylus 8 is attached to the flat portion '26 of the stylus rod.

A piano string is used as the resilient rod 24 which is connected to the other end of the stylus rod 23. In order to bring the resonant frequency of the stylus system thus constructed to a higher range, the stylus rod 23 is shortened. Then the resonant frequency of the stylus system becomes higher due to the large strength and small weight of the metal rod and the mechanical resistance of the vibration system for a lower frequency region is reduced due to the small diameter of the elastic rod 24, preferably the piano string which is connected to the stylus rod 23.

Moreover, the frequency characteristics can also be adjusted by changing the connection position of the stylus rod 23 and the armature 14. The desired part of the armature 14 can be pressed and deformed longitudinally or transversely to change the vibration mode of the deformed portion.

A heretofore known piezo-elernent in a cartridge has no supporting piece 17 as shown in FIGS. 6 and 7. Accordingly, when the displacement or the vibration of the stylus 8 due to the sound groove is transmitted to the piezo-electric element through the armature 14 the free end of the element will be apt to vibrate following the horizontal movement of the stylus. Hence the torsional movement can not well be transmitted so that a desired faithful electrical output can not be obtained.

But according to this invention, the free end of the element 1 is supported with a certain tension by the supporting piece 17 to the desired portion of the case so that the element 1 will not be apt to vibrate with the same movement as the horizontal movement of the stylus.

Accordingly the torsional movement which occurs around the axis of the supporting piece is faithfully transmitted to the element 1. Hence the disadvantage of the ordinary cartridge above mentioned can be eliminated by this invention. Besides a reproducing sound of higher frequency can be improved since the material having suitable hardness, resiliency and brake action such as nylon film sheet'is adopted for the supporting piece 17.

The above description has been mainly taken in connection with a ,Bimorph for a-pickup, but it will be apparent that the device according to this invention can also be applied to a cutter in which electric signals applied to a Bimorph are transformed to the corresponding mechanical vibrations.

It will be also understood by those skilled in the art that such a Bimorph and a single element can be applied for a device which can perform electro-mechanical transformation in the form of a matrix.

As will be understood from the foregoing description, the angle is so selected that the output voltage is proportional to the'sum of the difference of the two external forces applied to the piezoelectric element. In other words, the angle 0 is so selected that the output voltage is proportional to n(q+r) or to m(q-r), when q and r respectively represent two external forces and n denotes a transfer constant between the force and the voltage.

In the more general case the voltage n(q+ar) or n (q-ar) is obtained, where oz denotes a proportion constant between the forces q and r. The two external forces include not only the perpendicular force F, and shearing force F applied to the element, but also forces which are component forces of a'force applied to the element and which have been designated F and F When such two forces are applied to the element, it produces an output voltage which is proportional to the sum or the difference of the external forces.

It will be understood that many modifications and variations may'be' effected without departing from the scope of the novel conceptions of this invention.

What is claimed is:

1. A piezo-electric transducer device comprising two piezo el'ect'ric elements integrally laminated to each other 8.. with their two major axes being in the same plane, a first electrode secured at the interface between the lamimated-elements, a pair'of electrodes secured to theopposite faces of said elements in parallel spaced relation to said first electrode, means freely supporting one end of said laminated elements, each of said elements being responsive to both bending and'tor'sional forces applied thereto, driving means including a phonograph stylus arranged to be received in a -45 record groove, said driving" means being mechanically coupled to the freely supported ends of said elements to provide bending and torsionalforces along the entire exposed surface of said laminated elements, the angle of polarization ofone of said elements with respect to the major. axis of said element being different from the angle of polarization of the other of said elements, and defining an angle 0 with its major'axis which satisfies the following equation when bending and torsional forces are applied to the transducer:

cos 0 sin 0:: (cos 0-s'in 0) the relationship of the angles of polarization being such that one of the elements produces a voltage proportional to the sum of the amplitudes of the vertical and horizontal vibrations on said stylus, and the other element produces a voltage which is proportional to the difference of the amplitudes of the vertical and horizontal'vibrations on said stylus.

2. The device of claim 1 in which the angles of polarization of said elements are equal and opposite with respect to their major axes.

References Cited in the file of this patent UNITED. STATES PATENTS 

1. A PIEZO-ELECTRIC TRANSDUCER DEVICE COMPRISING TWO PIEZO-ELECTRIC ELEMENTS INTEGRALLY LAMINATED TO EACH OTHER WITH THEIR TWO MAJOR AXES BEING IN THE SAME PLANE, A FIRST ELECTRODE SECURED AT THE INTERFACE BETWEEN THE LAMINATED ELEMENTS, A PAIR OF ELECTRODES SECURED TO THE OPPOSITE FACES OF SAID ELEMENTS IN PARALLEL SPACED RELATION TO SAID FIRST ELECTRODE, MEANS FREELY SUPPORTING ONE END OF SAID LAMINATED ELEMENTS, EACH OF SAID ELEMENTS BEING RESPONSIVE TO BOTH BENDING AND TORSIONAL FORCES APPLIED THERETO, DRIVING MEANS INCLUDING A PHONOGRAPH STYLUS ARRANGED TO BE RECEIVED IN A 45-45 RECORD GROOVE, SAID DRIVING MEANS BEING MECHANICALLY COUPLED TO THE FREELY SUPPORTED ENDS OF SAID ELEMENTS TO PROVIDE BENDING AND TORSIONAL FORCES ALONG THE ENTIRE EXPOSED SURFACE OF SAID LAMINATED ELEMENTS, THE ANGLE OF POLARIZATION OF ONE OF SAID ELEMENTS WITH RESPECT TO THE MAJOR AXIS OF SAID ELEMENT BEING DIFFERENT FROM THE ANGLE OF POLARIZATION OF THE OTHER OF SAID ELEMENTS, AND DEFINING AN ANGLE $ WITH ITS MAJOR AXIS WHICH SATISFIES THE FOLLOWING EQUATION WHEN BENDING AND TORSIONAL FORCES ARE APPLIED TO THE TRANSDUCER: 